(1) Field of the Invention
This invention relates to specific, radiation-cured, coated abrasive products having novel patterned surface coatings useful in the ophthalmic, crankshaft and other fine finishing operations such as the sanding of automotive parts requiring a combination of controllable fine surface finishing and high cut rate.
(1) Description of the Prior Art
The so-called conventional manufacture of coated abrasive material requires, in general, the coating of a "maker" coat, i.e., a solvent or water-based adhesive composition, onto a backing member, followed by the application of grain thereto by electrostatic deposition. The curing of the maker coat, i.e., the adhesive or binder layer, to adhere the grain to that layer and the maker coat layer to the backing member is by thermal curing and, generally, requires a relatively long time, e.g., up to several hours in some cases. This is accomplished while passing the coated abrasive material through a loop dryer. While a loop dryer allows for long drying and curing times, the use of such is attendant with certain disadvantages such as the formation of defects where the material is suspended, sagging of the maker coat before it becomes sufficiently hardened and changing of the grain position due to the material being vertically suspended, variations in temperature and the resulting inconsistent cross-linking of the binder comprising the maker coat due to the necessarily slow air circulation.
In addition to the maker coat, a size coat is also generally applied over the abrasive grains, in the manufacture of conventional coated abrasive material, sometimes before the maker coat is completely cured. This coat also necessitates curing and passing of the coated abrasive material through a loop dryer due to the relatively long curing times required. Also, in some cases, the backing member, particularly if of cloth, need be provided with a so-called "back" coat and a pre-size coat, prior to the application of the maker coat. Thus, the conventional manufacture of coated abrasive material requires not only a considerable time for thermal curing of various coatings involved in its manufacture, but also, as earlier pointed out, is accompanied with certain necessary defects resulting from the manner of manufacture involved.
In somewhat more recent times, it has been suggested that a reduction in the manufacturing time for coated abrasive material could be achieved through curing of the various coating materials involved by electron beam radiation. Thus, in U.S. Pat. No. 4,047,903, which issued on Sept. 13, 1977 to Hesse et al. there is disclosed coated abrasive material which is manufactured by coating a backing member with at least one base layer of a binder resin hardenable by irradiation, at least one intermediate layer of abrasive grains, and at least one top layer of binding resin hardenable by irradiation. The binder resin comprises, in general, the reaction product of a polycarboxylic acid with an esterified epoxy resin, prepared by the reaction of an epoxy resin with a member selected from the group consisting of acrylic acid and methacrylic acid and the reaction product of such an epoxy resin first reacted with diketenes and then reacted with a chelate forming compound. Although the binder system is different than found in the conventional coated abrasive materials, the construction is much the same. Neither is there any suggestion by Hesse et al that patterned surface coatings can be obtained.
Subsequently, in U.S. Pat. No. 4,457,766, which issued July 3, 1984, on an application filed Oct. 8, 1980, and which is now assigned to Norton Company, the Assignee of the instant application, there was disclosed another binder system for use in the manufacture of coated abrasive material. Such a binder system comprises, in general, an oligomer, a diluent, fillers and minor amounts of other additives, the various components being selected in each case to give the desired physical properties to the coated abrasive material manufactured. The oligomer selected, as disclosed by the patentee, can be any reactive polymer which gives the desired properties to the backing member and the coated abrasive material. Suitable electron beam curable materials disclosed are urethane-acrylates and epoxy-acrylates. Particularly preferred are the diacrylate esters such as the diacrylate esters of bisphenol-A epoxy resin. Among the diluents disclosed, which are disclosed by the patentee to be utilized to adjust the viscosity of the binder so as to be suitable for the various coating methods to be used, are the vinyl pyrrolidones and the multifunctional and monofunctional acrylates. The compounds that are disclosed to be preferred by the patentee are N-vinyl-2-pyrrolidone (NVP); 1,6 hexanediol diacrylate (HDODA); tetraethylene glycol diacrylate (TTEGDA); and trimethylopropane triacrylate (TMPTA). "Such materials have been found by the patentee to be not only successful when used in adjusting viscosity and controlling flexibility, but also when used in reducing the radiation required for curing." The coated abrasive materials disclosed, nevertheless, are of the conventional type long manufactured except that an electron beam curable binder is used. Thus, a cloth backing member may be provided with a back and face fill of the binder, as conventionally done, and partially cured prior to application of a maker coat, all of which may comprise the same components but in somewhat different formulation. Following application of the maker coat, abrasive grain is applied to the maker coat and the maker coat is then cured by electron beam through the backing member. The size coat of similar formulation as the maker coat is then applied and cured. Patterned surface coatings are not disclosed or even suggested.
In U.S. patent application Ser. No. 474,377, filed in the United States Patent and Trademark Office on Mar. 11, 1983 by Stanley J. Supkis, Jr., Richard A. Romano, and Walter A. Yarbrough, now abandoned, and assigned to Norton Company, the Assignee of this application, there was disclosed coated abrasive material in which the adhesive was cured by exposure to ultraviolet ("UV") light. Prior to the invention disclosed in that application, it appeared to be generally believed that the relatively thick adhesive coatings typically required for coated abrasives, as compared with most decorative surface coatings then being UV light cured, would be very difficult, if not impossible, to cure by UV light, due to the limited depth of penetration of such light. Therefore, most of the workers in the field of coated abrasives are believed to have concentrated on electron beam curing instead, as exemplified by the earlier-mentioned U.S. Pat. No. 4,457,766.
As disclosed in application Ser. No. 474,377, the coated abrasive manufacturing process, in general, involves coating an abrasive grain and adhesive slurry onto a suitable backing member, rather than the conventional technique of applying a maker coat to a backing member, followed by electrocoating abrasive grain, and then application of the size coat. The adhesive grain slurry in U.S. Pat. No. 474,377 comprises, in general, three classes of components, namely, acrylate monomer, photoinitiator, and abrasive grain. Other components, however, may optionally be present. As disclosed by the inventors in that application, it is necessary to utilize substantial amounts of acrylate monomers containing three or more acrylate groups per molecule. Typical commercial products of this type, as disclosed, are trimethylolpropane triacrylate ("TMPTA") and pentaerythritol triacrylate ("PETA"). Nevertheless, if somewhat less brittle cured products are desired, difunctional acrylate monomers, e.g., 1.6-hexanediol diacrylate ("HDODA"), are included in the dispersion as well. The relative amounts of such di- and tri- functional acrylates must be adjusted, along with those of the other components in the slurry, to give proper viscosity for coating as well as acceptable characteristics for the cured film. Optionally, for further adjustments of the rheology of the slurry as coated and the toughness and cutting characteristics of the cured product, higher molecular weight acrylate oligomers are normally used in addition to the acrylate monomers noted above. The preferred oligomers, as disclosed in application Ser. No. 474,377, are the diacrylates of bis-phenol A type epoxy resins and the di- to octo-acrylates of novolak phenolic resins prepared by the condensation of bis-phenol A or other similar di-phenols with formaldehyde. Other optional components disclosed for inclusion in the slurry are organosilanes and organotitanates for improving the bond between the adhesive and abrasive grain. Further, the inventors disclose that organic tertiary amines, the preferred being N-vinyl pyrrolidone ("NVP") can also be added to the formulation to promote adhesion. NVP also, as disclosed, serves as a reactive viscosity-reducing diluent. Actually, it is believed that NVP is a cylic amide rather than an amine derived from a tertiary amine. Nevertheless, as disclosed later on, such components in proper amounts is an essential part of this invention. Although slurry coating is disclosed in this application, contrary to the conventional manufacture of coated abrasive material, the disclosure is not concerned with patterned coatings.
Subsequently there was disclosed in U.S. patent appln. Ser. No. 680,619, filed Dec. 9, 1984, and which is a continuation-in-part of Ser. No. 474,377, that conventional coated abrasive materials can also be manufactured using UV light curable adhesive compositions. Thus, where a conventional coated abrasive material is to be manufactured, the maker coat comprises, in general, an acrylated oligomer, the preferred one being Celrad.RTM. 3700, a commercially available diacrylate of epoxy resin of the bisphenol A type and having an average molecular weight per acrylate unit of about 275, a photoinitiator, a thermal initiator, NVP, a viscosity reducer (vinyl acetate) capable of copolymerizing with the acrylated oligomer, and importantly, an amine adduct of an acrylated monomer. The preferred such amine adduct, as disclosed in the application, resulted from the reaction product of 1-octyl amine and TMPTA. The amine adduct provides better adhesion of the maker coat to the coated abrasive backing member. The thermal initiator was added to the maker coat composition whereby curing of the inner part of the adhesive layer was accomplished. The cure initiated by the UV light was found by the inventors to be fully effective only in the outer part of the maker coat layer particularly where the coated abrasive material used abrasive grain which strongly absorbs UV light. Patterned abrasive coatings, however, are not disclosed in this application.
In U.S. patent application Ser. No. 735,029, which was filed on May 17, 1985 by Stanley J. Suphis, Jr., Eugene Zador, Sitaramaiah Ravipate, Richard A. Romano, and Walter A. Yarborough, and which is a continuation-in-part of application Ser. No. 680,619, above-mentioned, there is disclosed coated abrasive material of conventional manufacture having harder product cures. With such products, the maker and size coats, as disclosed, each comprises, in addition to various other components, acrylated monomers with four or more acrylate groups per molecule, e.g., dipentaerythritol hydroxy pentacrylate ("DPHPA"). Additionally, the size coat includes a diacrylate of an ester-linked urethane oligomer, e.g. Urethane 783, a commercially available diacrylated polyester urethane oligomer with an average molecular weight of about 5500. The manufacture of such conventional coated abrasive material is accomplished, in general, by application of the maker composition to the backing member, followed by electrocoating of the abrasive grain, after which the maker coat is rapidly cured by exposure to UV light. Next, the size coat is applied, and such is then rapidly cured by further exposure to UV light. Patterned abrasive coatings are not disclosed.
The complete disclosures of applications Ser. Nos. 474,377; 680,619; and 735,029, all above-mentioned, are incorporated herein by reference.
The manufacture of coated abrasive material characterized by various patterned surface coatings of abrasive material has long been disclosed by those in the art. Examplary of prior art patents showing such abrasive coatings are U.S. Pat. Nos. 1,657,784; 2,108,645; 3,605,349; and 3,991,527. In U.S. Pat No. 1,657,784, there is disclosed a coated abrasive material in which various adhesive patterns can be provided on a backing member by means of a roll coater, followed by application of grain to the adhesive coating before it hardens. The desired pattern can be provided in relief on the roll or cylinder used in the adhesive coating. In general, the pattern consists of regular and uniform alterations of abrasive and non-abrading portions with definite channels for the exit from the abrading surface of the dust or particles produced by the abrasion operation.
U.S. Pat. No. 2,108,645 discloses coated abrasive material in which a backing member is provided with an intermittent or discontinuous coating of adhesive. This is accomplished by passing the backing member between two rollers, one of which is smooth and rotates in an adhesive bath. The other roller has a pattern of depressed portions thereon each surrounded by a raised portion. The portion of the backing member which comes opposite the depressions receives adhesive from the smooth roller while that coming under the raised portions receives relatively little. Thus, there results, when abrasive grain is applied, essentially a pattern of islands of abrasive grain surrounded by areas or channels with little or no grain stuck to the backing member.
In U.S. Pat No. 3,605,349, there is disclosed an abrasive finishing article comprising, in general, a backing member, on the surface of which is provided a pattern of islands of abrasive, resulting in channels for circulation of slurry. The abrasive articles can be manufactured by various means one of which involves the use of a roller on the periphery of which are provided raised "islands" or lands, e.g., in diamond shape. The abrasive mixture is first transferred to the roller having the diamond-shaped pattern provided thereon by a smooth roller which rotates in an adhesive bath and which peripherally contacts the patterned roller. The patterned roller then transfers the pattern of abrasive material onto the backing member. Thus, in effect, the diamond-shaped pattern is printed onto the backing member.
The pattern on the coated abrasive material disclosed in U.S. Pat. No. 3,991,527 results from transferring geometrical-shaped patterns of adhesive binder onto a backing member, followed by application of abrasive grain to the adhesive. The adhesive, in one manner of manufacture, is transferred by a smooth roller, rotating in an adhesive bath, to the patterns provided on the patterned roller which, in turn, transfers adhesive in the shape of the pattern to the backing member. As disclosed by the drawings in this patent, the pattern produced comprises what one might call islands of abrasive. And, the islands are surrounded by rightangularly intersecting channels which open onto the outer or peripheral edge of the abrasive discs provided from the abrasive material.
The use of intaglio or rotogravure rolls in various coating processes, including the manufacture of coated abrasive material is well known. Such rolls are provided with various patterns of cells, or wells as they are sometimes called, cut into the surface of the perimeter of the roll, the cell pattern provided and the capacity thereof depending somewhat upon the particular coating application. In general, when such a roll is used in a coating application, it rotates in a pan of the coating material and, as it rotates through the coating material, the cells are loaded up with the coating material much like a bucket conveyer. After the gravure roll rotates out of the pan and before it contacts the backing member onto which the coating material is to be transferred, its surface is wiped with a knife or doctor blade. Thus, only the material contained in the cells is available for coating of the backing member. The amount transferred depends, in general, upon the total theoretical volume of the cells and the particular material that is being coated. As a result, gravure rolls are commonly used when it is desired to apply a controlled amount of coating material to a backing member. Also, such rolls are commonly used when it is desired to provide a particular pattern of coating material onto a substrate. In such a case, cells the shape of the pattern desired in the coating to be provided will be provided in the peripheral surface of the gravure roll. Thus, if it is desired to coat a design having a hexagonal shape onto a substrate, a gravure roll having such a design cut in its surface will be used. Nevertheless, such a roll is not expected to transfer merely an outline of such a design.
Prior to the invention disclosed in this application, others have disclosed the manufacture of coated abrasive material in which a slurry of a radiation curable binder and abrasive grain is applied to a backing member using a gravure roll. Thus, in U.S. Pat. No. 4,644,703, which issued Feb. 24, 1987 to Norton Company, the Assignee of this patent application, there is disclosed coated abrasive material suitable for one step fining of plastic ophthalmic lenses. Such a product is manufactured by coating two distinct layers of an adhesive/abrasive grain slurry onto a backing member, to provide a coarse outer layer and a finer inner layer of abrasive grains. The slurry coatings in that patent are deposited by a gravure roll having a trihelical pattern cut therein which, in turn, imparts a pattern of parallel lines of adhesive/abrasive grain slurry to the backing member and, in turn, to the first deposited coating. Subsequent to application of the first coating, the backing member with the wet slurry thereon passes through a texturing bar assembly whereat the continuity of the deposited coating material, i.e., the lines of wet slurry, is broken up to provide a somewhat discontinuous pattern. Afterwards, the wet slurry coating is subjected to ultraviolet light to cure the adhesive binder and to adhere the abrasive grains to the backing member. After curing of this first coating, a second adhesive/abrasive grain slurry is coated onto the first coated backing member, to provide the outer grain layer in the coated abrasive product. This processing is the same except that a gravure roll having a different helical pattern is used, and there is no texturing of the second applied wet slurry. The abrasive grains are adhered to the backing member, which may be a polyester film, with binders compounded primarily of acrylates in somewhat different formulations for the respective first and second coats. The radiation curable binders, in general, comprise a mix of triacrylated monomers, e.g., trimethylolpropane triacrylate (TMPTA), diacrylated monomers, e.g., hexanediol diacrylate (HDODA) and acrylated oligomers, the preferred being the diacrylates of epoxy resins of the bisphenol-A type. Importantly, also, the patentees disclose including in the adhesive formulations unsaturated organic amines, e.g. N-vinyl pyrrolidone ("NVP"), in a controlled amount to promote adhesion. Although a gravure roll is used in the manufacture of the coated abrasive material disclosed, such roll functions as usual. It deposits a slurry coating of parallel lines as reflected by the pattern cut in the roll surface.
U.S. Pat. No. 4,773,920, which issued to Chasman et al on Sept. 27, 1988, discloses a coated abrasive material suitable for lapping operations including second fining applications for ophthalmic lenses. The coated abrasive material is manufactured by coating a suspension of abrasive grain in a radiation-curable binder onto a backing member such as polyester film. The binder can comprise radiation-curable monomers, as believed disclosed earlier by others above-mentioned, and, optionally, reactive diluents. Of the monomers that are disclosed to be useful, the patentee discloses that such should contain two ethylenically unsaturated moities therein, e.g., hexane diol diacrylate. The preferred radiation curable "monomers", as disclosed, include oligomers selected from urethane acrylates, isocyanurate acrylates, polyester-urethane acrylates and epoxy acrylates. As reactive diluents, the patentees disclose trimethylolpropane triacrylate (TMPTA) and also hexane diol diacrylate. It is preferred, according to the patentees, that a coupling agent, e.g., gamma methacryloxypropyl trimethoxy silane, be included with the monomer to promote adhesion between the abrasive grains and the cured binder. Nevertheless, the patentees disclose that it is also preferred that such silane be coated on the abrasive grain prior to dispersion of the grains in the binder. Rotogravure coating is disclosed to be preferred by the patentees for the reason that the rotogravure coater can impart a uniform pattern of ridges and valleys to the binder composition, which, after the composition is cured, can serve as channels for flow of lubricants and for removal of abraded material. Nevertheless, the patentees fail to disclose any particular gravure roll or the pattern provided therein. Moreover, none of the examples in the patent disclose the use of a gravure roll, even though such is disclosed as preferred. Thus, it is believed that the patentees merely speculate that use of a gravure roll would impart a pattern of ridges and valleys to the binder composition, i.e., a reflection of the design cut in the roll surface, much like the islands of abrasives and channels obtained by those earlier in the prior art.
The expression "ophthalmic lens fining", when it is performed with coated abrasive material on a Coburn-505 fining machine, can refer to a simple "one-step" process or it can denote a more complex "two-step" operation. In one-step fining, a single daisy wheel or film backed fining pad ("Snowflake") is employed before the final slurry-polishing. Such a pad is capable of removing relatively large amounts (0.4-0.6 mm) of excess stock and, at the same time, generate a sufficiently fine, scratch-free surface. In the more common two-step operation, a silicon carbide coated abrasive product (a first fining pad) is used first which removes most of the surplus stock. This is followed then by use of a second-fining pad, a much finer grain, aluminum oxide based, coated abrasive product. This second pad removes little stock (0.03-0.05 mm) but has fine finishing capabilities. Preference for the one-step or the two-step process depends on a number of factors which include the lens type used (glass, CR-39 plastic and polycarbonate are the three most common lens types), the lense curvature (diopter), shape (cylindrical and spherical), and lens size. One-step lens fining is most common with plastic lenses of relatively low diopter and of medium (e.g. 65 mm) size.
In either case, the main objective of lens fining is to prepare the lens for the final or slurry polishing step which is usually performed with slurries of various small particle size aluminum oxide (0.5-1.0 micron range). As a consequence of such low particle size, the slurries cannot remove deep scratches (Rt values greater than, say, 50-70 microns) from lenses obtained during the fining process. Therefore, there is always a need for products that improve the results of the fining or prefinishing process thus reducing the burden, both time and in fine polishing requirements, placed on the slurry-polishing step.
A description of the fining process and of suitable machinery for accomplishing it are disclosed in U.S. Pat. Nos. 3,732,647 (to Stith) and 4,320,599 (to Hill et al), the complete specifications of which are herein incorporated by reference. Stith discloses in FIG. 2 of the patent, a lapping tool such as envisioned by one aspect of the instant invention. The lapping surface 78 of the tool provided in Stith may be a coated abrasive material consisting of abrasive grains adhered to a flexible backing which, in turn, is supported by the structure disclosed in Stith.
Recently there has become available commercially a second fining pad which is characterized by spaced-apart spherical-shaped aggregates of aluminum oxide abrasive grain (3-4 microns) on a backing member. The abrasive grains are held together in the aggregate and the aggregates to the film backing member by a phenolic binder system. During the fining operation, the aggregates are supposed to break down and the fine abrasive particles are then liberated. These liberated abrasive particles are believed responsible for the fine finish obtained.
Although this most recently introduced second fining pad is characterized by its good cut rate and finishing qualities, its use nevertheless is attendant with certain disadvantages. The abrasive aggregates have to be manufactured in a separate process adding cost and quality control problems to the manufacture of the final product. Moreover, although the aggregates are supposed to break down uniformly during the fining process, yielding a quantity of fine grain particles and, ultimately, a more finely finished lens, uniform aggregate breakdown does not always appear to be accomplished in use. Oftentimes, we have discovered, whole aggregates are torn out of the coating under the prevailing pressure (20 psi) in the lapping tool used, leaving holes in the coating which then can cause uneven finishing. Moreover, the binder system is solvent-based, leading to certain problems, as above-disclosed, in addition to polluting the atmosphere.